1. Field of the Invention
The present invention relates to imaging apparatuses and imaging methods, and particularly to an imaging apparatus and an imaging method that are capable of imaging a sample using Talbot interferometry.
2. Description of the Related Art
With Talbot interferometry, it is possible to obtain a phase image of a sample using interference of light of various wavelengths, including X-rays. A Talbot interferometer is an instrument that can generate phase images using the Talbot effect.
Examples of methods for imaging a sample using Talbot interferometry include a method in which an imaging apparatus having a source, a diffraction grating, an absorption grating, and a detector is used to obtain a phase image of a sample. An overview of this method will now be described.
First, the incident light from the source is transmitted through the sample and changes its phase. After transmitted through the sample, the light is diffracted by the diffraction grating and forms an interference pattern on a plane apart from the diffraction grating. The interference pattern contains phase information of the sample. When the absorption grating is placed at a position where the interference pattern is formed, the interference pattern is partially blocked and a moiré pattern appears. The moiré pattern is detected by the detector. By computing and analyzing the detection result, a phase image of the sample can be obtained.
There are several ways to obtain a phase image of a sample from the moiré pattern. One of them is a phase stepping method in which an absorption grating is moved relative to an interference pattern to change and detect moiré multiple times, and then the phase is calculated from results of the multiple times of detection.
As a way to move an absorption grating relative to an interference pattern, Japanese Patent No. 4445397 (corresponding to U.S. Pat. No. 7,180,979) describes a method which involves changing a relative position of a diffraction grating and an absorption grating. Also, Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2008-545981 (corresponding to U.S. Pat. No. 7,889,838) describes a method which involves moving a light source or source grating configured to split light from the light source into narrow beams.
As described above, Japanese Patent No. 4445397 describes a method in which imaging is performed while the relative position of the diffraction grating and the absorption grating is changed. To carry out this method, it is necessary, each time imaging is performed, to change the relative position of the diffraction grating and the absorption grating by a distance obtained by dividing a period of the absorption grating by the number of times of imaging. For example, when Talbot interferometry is performed using X-rays as light, the moving distance of the diffraction grating or the absorption grating is about several micrometers. Therefore, it is necessary to move the diffraction grating or the absorption grating with high precision such that movement is controlled below the micrometer scale.
Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2008-545981 describes a method which involves moving or rotating the source or the source grating. In this method, the moving distance of the source or the source grating for each imaging is about ten times larger than that in the method which involves moving the diffraction grating or the absorption grating.
However, when the source or the source grating is moved, the direction of light incident on a sample is changed with respect to the sample. This is equivalent to a positional displacement between the sample and a detector. Therefore, as the source or the source grating is moved, the light intensity distribution on the detection surface of the detector is displaced and hence, the resulting phase image of the sample may be blurred.